The present disclosure relates to a device for generating a beam or column of light with uniform intensity. This device is useful in quality control systems and for other applications needing uniform intensity in a light beam.
In an electrostatographic, electrophotographic or xerographic printing apparatus, an imaging member or photoreceptor comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation, for example light, which selectively dissipates the charge in certain areas of the photoconductive insulating layer to create an electrostatic latent image. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles, for example from a developer composition, on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving substrate such as paper. The photoreceptor is generally in the form of a cylindrical drum, with the photoconductive surface being the circumferential surface of the drum.
Current quality control tools for verifying the quality of imaging apparatus components use expensive and high maintenance exposure systems. Such tools typically include filtered halogen or xenon sources with bulky optics and require frequent calibration and maintenance. Light-emitting diode (LED) bars can be used as an exposure source. However, LED bars are difficult to implement in a fixture that is adjustable for measuring multiple drum diameters and lengths while avoiding mechanical interference. Light from these sources is shined upon the photoreceptor drum during the quality control process.
Requirements for the light exposure system of the quality control testing system are very stringent. High uniformity is required along the photoreceptor drum axis. Perpendicular to this axis, i.e. in the circumferential or process direction, the beam cannot diverge. The beam must be narrow, both to minimize stray light and to minimize changing transmission at the air/transport layer interface due to the changing incident angle of the curving surface of the photoreceptor drum. A narrow beam is also required for the underfill requirement of the calibrating detector.
The best uniform light exposure sources are obtained through integrating spheres. An integrating sphere is a hollow spherical cavity with a reflective interior, with small holes for entrance and exit ports. Light rays incident on any point on the inner surface are, by multiple scattering reflections, distributed equally to all other points, so that the exiting light is uniform. However, the drawback is the heavy loss of power and large divergence (increase in beam diameter with distance from the aperture) at the exit port. As a result, either the test surface has to be brought close to the exit port or the light needs to be captured by some means, such as fiber bundles. However, this has been found to be impractical in practice, because the fiber bundles must be very large to provide a rectangular exit aperture. This large size in turn cuts down the integrating sphere throughput efficiency. In addition, the intensity may fluctuate if the fibers are moved, even in the case of multimode fibers that reduce modal hopping.
It would be desirable to develop new devices for that can generate light of uniform intensity.